|How do the W100s compare to the 580 in bass extension, treble smoothness, and timbral accuracy (my 3 main criteria)?
favourably. Very favourably. To my ears, the W100 is better in every regard. Easily.
I have always said that the W100 needs lots of break-in. Some are impressed with the W100's performance right away, some like it after 100 hours and some have even found that it took them 400 hours to fall in love. There is a possibility of production variance, wood is a natural, organic material after all. But I suspect that the specific nature of the break-in process has a lot to do with those differences as well.
I'd recommend breaking it in at normal or slightly above normal levels. In my experience, it might not be all that helpful if one creates operating conditions that are rather unusual - if one plays the headphone very loud or for very long periods, days on end.
The W100 has a brighter tonal balance than the Beyer 770 Pro, but, to my ears, it is not as bright as the Senn HD600 or the AKG K501. In order to improve the W100's bass extension and impact, I'd play some recording with a lot of low and slamming bass content through it, for several hours straight or overnight (but not excessively loud!). I would be very surprised if things didn't improve. And as far as the treble is concerned, the W100 has more upper mid response than the Beyer 770 Pro, its soundstage is closer to the listener, but to my ears, it is a lot smoother and homogenous than any other headphone I have ever listened to, including the Beyers, Senns or AKGs. It is possible that the individual shape of our ears or individual differences in our ear canal resonance frequency play a role in this. I don't know. However, I have noticed that the W100 seems somewhat sensitive to placement. I prefer wearing it forward, with the pads touching the rear of my earlobes. And there is JML's conehead mod, of course: carefully bending the two connecting tubes to achieve a slightly tighter fit. This will improve the W100's bass extension and will shift its tonal balance a little lower. BTW, using my EMP for both the 770 Pro and the W100, I prefer the W100's bass performance. It's tighter, more tuneful, has greater timbral accuracy, it's musically more convincing to me.
calanctus, please, just don't give up!